The single FIGURE in the attached drawing provides a very schematic representation of the general configuration of an example of an electromechanical actuator of the rotary-linear type with which the invention is concerned. As a succinct reminder, such an actuator comprises:                a casing 1;        rotary electric motor means M comprising at least one field winding; and        at least one nut 2 rotatably supported in bearings 3 of said casing 1 and integral in rotation with said motor means M.        
In the example more specifically shown, which corresponds to a rotary-linear actuator of the direct drive type:                the rotary electric motor means M, that are of an electromagnetic type, comprise electric windings or field windings 4 that are arranged in a ring and are supported in particular in at least one slot 5 provided in the casing 1 or in a frame integral with the latter, the assembly constituting a stator, and that are capable of generating a rotating field driving in rotation a rotor arranged coaxially inside the ring of windings 4; and        the at least one nut 2 is arranged coaxially inside the ring of windings 4 constituting the abovementioned rotor, this nut 2 being able to be equipped with magnets, typically with permanent magnets, so as to be driven in rotation in the bearings 3 by the rotating field.        
Moreover, the actuator comprises:                at least one actuator rod 6 arranged substantially coaxially with the nut 2, said nut 2 and said actuator rod 6 being coupled in rotation by axial helical meshing means; to this end, as shown in the FIGURE, the nut 2 is presented in the general form of a tubular element the inner surface of which is, over at least part of its length, provided with at least one helical thread 7, whilst the actuator rod 6 has one end inside the nut 2, which can be a widened portion 8 as illustrated, which is provided with a helical thread 9 on the outside;        means 17 for locking the actuator rod 6 in rotation relative to the casing 1 so that the rotation of the nut 2 leads to a linear displacement of the actuator rod 6; said means for locking in rotation can simply be constituted by a key 10 arranged substantially coaxially with the nut 2 and extending axially, said key 10 having a non-circular section (for example polygonal, in particular square) and having one end 11 embedded in the casing in fixed manner and its other end 12 engaged sliding freely in an axial bore 13 in the actuator rod 6;        means provided on the casing 1 for fastening said casing 1 to a fixed or displaceable component; for example one (or more) part(s) of the casing 1, such as in particular the end 14 of the casing 1 opposite the protruding part of the actuator rod 6 and which can for example be in the form of a clevis, is equipped with an eyelet 13 capable of receiving a coupling element;        means provided on the actuator rod 6 for fastening the free end 15 of said actuator rod 6 to a component which is respectively displaceable or fixed; a simple solution is for said end 15 of the actuator rod 6 to be equipped with an eyelet 16 capable of receiving a coupling element.        
Of course, the above description is given only as an indication to give an idea, it being understood that numerous embodiments of rotary-linear-type actuators exist or can be envisaged; in particular, a double actuator can be derived from the structure previously described by providing, in the ring of windings 4, two nuts 2 arranged end to end and having respective reverse pitch threads or a single nut with two successive reverse pitch threads, with which two opposite actuator rods engage. Moreover, the term thread must be understood in a broad sense, as being able to denote a standard trapezoidal screw as well as a ball screw or a roller screw.
Electromechanical actuators of the rotary-linear type are nowadays used in particular (although not exclusively) in equipment on so-called “all-electric” modern aircraft. The design of an “all-electric” aircraft involves eliminating the hydraulic systems and controls used up till then and replacing them with electromechanical solutions involving electromechanical actuators and in particular electromechanical actuators of the rotary-linear type. The electromechanical actuators of the rotary-linear type used in this context can serve, for example, to drive the aircraft's stabilators (wing flaps, flight control surfaces etc.).
Of course, the electromechanical solutions thus put into place must offer a degree of dependability at least equal to that of the previous hydraulic solutions. The dependability analysis highlights the following failures:                breakage of the mechanical linkage,        fouling of the surface,        seizing of the surface.        
The first two failures mentioned are not characteristic solely of electromechanical actuators of the rotary-linear type and can occur with other solutions (for example the previous hydraulic solutions). Solutions are therefore known for dealing with these problems, solutions which can be repeated in the case of electromechanical actuators of the rotary-linear type.
By contrast, the third failure mentioned (seizing of the surface) is characteristic of electromechanical actuators of the rotary-linear type, and it is essential to prevent seizing of such an actuator, or at the very least be informed of its occurrence.
The invention is based on the fact that seizing does not appear suddenly and that it leads to a gradual degradation of blocking performance, and therefore a deterioration of performance, of the actuator. The invention is therefore based on detection of the advance warning signs of seizing.
Conversely, this implies that, if sudden seizing of the actuator is possible, the means proposed in the context of the present invention are ineffective in providing any advance warning of the occurrence of the sudden seizing.